In-situ regulation of acid sites on Mn-based perovskite@mullite composite for promoting catalytic oxidation of chlorobenzene.

A series of Sm-Mn perovskite@mullite composites with different amounts of acid sites were successfully synthesized by regulating the level of in situ etched-surface modification. X-ray diffraction (XRD) test showed that the crystal structure of catalyst gradually changed from perovskite to perovskite@mullite composites and mullite. The characterization of temperature programmed desorption with ammonia (NH3-TPD) confirmed the acid sites on the surface of catalyst can be deployed by the in-situ modification. The temperature-programmed reduction with hydrogen (H2-TPR), and N2 adsorption-desorption showed that the surface modification also increased the reducibility, surface area, and mesoporosity of catalyst. The catalytic activities were compared by a long-term catalytic oxidation of chlorobenzene evaluation for 20 h of uninterrupted reaction at a relatively low temperature of 300 °C, and the Sm-Mn perovskite@mullite composite (SMPM-1.2) possessed the best catalytic stability. The X-ray photoelectron spectroscopy (XPS) measurement determined that the high ratios of lattice oxygen and tetravalent manganese did not improve the stability of catalyst in the catalytic oxidation of chlorobenzene, but the activities trends of samples were consistent with the change of surface (Mn4++Mn3+)/Mn2+ ratios. Meanwhile, the catalytic experiments for benzene, toluene, o-xylene and acetone showed that the as-prepared catalyst was also suitable for the efficient removal of the different types of VOCs. This work supplied a method for the further development of high activity catalysts for the removal of VOCs.